Aqueous ophthalmic solutions are typically applied to eyes in the form of drops, or used to treat contact lenses that are then subsequently placed in the eye. The primary functions of these solutions are to provide a moisturizing effect for eyes, or to clean, disinfect or wet contact lenses. Given these primary functions, ophthalmic solutions will include one or more surfactants that function as cleaning agents. The surfactants, however, also affect the surface tension properties of aqueous solutions, and in general, will increase the tendency of the solutions to foam. As used herein, a foam is a dispersion of a gas bubbles that form or are present in an aqueous ophthalmic solution. The gas bubbles are separated from the liquid by thin liquid films called lamellae. Ordinarily, the bubbles will burst at a thickness of approximately 10 nm, and this phenomenon is referred to as drainage. Drainage occurs almost instantaneously in pure water. On the other hand, surfactants tend to stabilize the lamellae against rupture, thereby facilitating foam formation and increasing foam stability in aqueous solutions.
The foam-forming tendency and foam properties are dependent on the type and concentration of surfactant in the solution. For example, surfactants that enhance foam formation include several members from the family of polyethers known as Pluronic® and Tetronic® surfactants. In particular, Pluronic® F-127 and Tetronic® 1107 are conventionally used as cleaning agents in ophthalmic solutions. Even at relatively low concentrations, e.g., less than 1% by weight, Pluronic® F-127 and Tetronic® 1107 surfactants can cause ophthalmic compositions to foam. U.S. Pat. No. 6,790,816 indicates that undesirable amounts of foaming can be avoided in compositions containing Tetronic® 1107 by simply reducing the amount of agitation of such products. See, also U.S. Patent Publication No. 2002/0141899.
Formulating aqueous ophthalmic solutions to minimize foaming can present a challenge from the perspective of both manufacturing and consumer satisfaction. For example, solution foaming increases production costs by reducing manufacturing process throughput and material handling speeds. Ophthalmic solutions that foam can also cause product handling to be more difficult for the consumer.
Octoxyglycerin (3-[(2-ethylhexyl)oxy]-1,2-propanediol), sold under the trade name Sensiva® SC50 (Schulke & Mayr), is a glycerol alkyl monoether known to be gentle to the skin. Octoxyglycerine is said to exhibit antimicrobial activity against a variety of Gram-positive bacteria associated with perspiration odor, such as Micrococcus luteus, Corynebacterium aquaticum, Corynebacterium flavescens, Corynebacterium callunae, and Corynebacterium nephredi, and is used in various skin deodorant preparations at concentrations between about 0.2 and 3% by weight (Sensiva® product literature, Schulke & Mayr).
U.S. Pat. No. 5,885,562 to Lowry et al., describes deodorant compositions comprising an antimicrobial agent, namely polyhexamethylene biguanide at a concentration of between 0.01% and 0.5% by weight, together with a polarity modifier such as Sensiva® SC50 at concentrations of 1% to 15% by weight. The compositions can also comprise a short chain monohydric alcohol such as ethanol from 20% to 80% by weight. U.S. Pat. No. 5,516,510 by Beilfuss et al. also describes deodorant compositions that comprise glycerin monoalkyl ethers, and in particular, octoxyglycerin. The deodorant compositions are said to be formulated in aqueous or alcoholic solutions and can include additional antimicrobial compounds, including triclosan, chlorhexidine salts, alexidine salts, biguanides and phenoxyethanol.